1. Field of the Invention
The present invention relates to a composite substrate manufacturing method and a composite substrate.
2. Description of the Related Art
Hitherto, a surface acoustic wave device is known which employs a composite substrate including a support substrate and a piezoelectric substrate bonded to each other, and which has comb-shaped electrodes formed on the surface of the piezoelectric substrate and being capable of exciting surface acoustic waves. By bonding, to the piezoelectric substrate, the support substrate having a smaller thermal expansion coefficient than the piezoelectric substrate, changes in dimensions of the piezoelectric substrate depending on temperature changes are suppressed, and changes in a frequency characteristic when used as the surface acoustic wave device are also suppressed. For example, a surface acoustic wave device disclosed in Patent Document 1 has a structure that a piezoelectric substrate and a support substrate are bonded to each other by using an adhesive layer. In the disclosed surface acoustic wave device, the occurrence of the spurious is suppressed by forming minute asperities on a surface (rear surface) of the piezoelectric substrate at which the piezoelectric substrate is bonded to the support substrate. More specifically, bulk waves are generated as one type of acoustic waves along with the surface acoustic waves near the comb-shaped electrodes and then reach the rear surface of the piezoelectric substrate. However, the bulk waves are scattered by the asperities formed in the rear surface. Thus, the bulk waves are avoided from reaching the comb-shaped electrodes after being reflected at the rear surface of the piezoelectric substrate, whereby the occurrence of the spurious is suppressed.